The present invention relates to an apparatus and method for mixing by agitation, and more particularly to an apparatus and method applicable to a wide variety of uses involving the mixing of a powder and a liquid by agitation.
In mixing processes which include adding a liquid to a powder, adding a powder to a liquid, or simultaneously adding a powder and a liquid, secondary agglomerates (“lumps”) of the powder are often produced in the liquid, and, once they have been produced, it is usually extremely difficult to re-dissolve these lumps in the liquid.
Accordingly, in recent years apparatuses and methods for uniformly mixing powder and liquid while avoiding generation of secondary agglomerates during mixing of the powder and the liquid have been suggested.
In Japanese Patent Laid-Open Publications No. Hei 11-19495, No. 2001-62273, and No. 2002-166154, a continuous mixing device is disclosed. In the continuous mixing device, a rotary disc is installed in a casing to which, in an upper part thereof, supply ports for feeding a liquid and a powder are attached, and in a lower part thereof, a drain port is attached. The rotary disc separates the inside of the casing into an upper mixing chamber and a lower mixing chamber. Further, a scraper is attached to an upper area of the rotary disc, and a revolving scraper, which revolves independently of the rotary disc in a noncontact manner, is mounted at a position below the rotary disc. A powder and a liquid fed from the supply ports are mixed by rotating the rotary disc, and a resultant mixture moved into the lower mixing chamber is scraped off while being mixed so as to be transported continuously to the outside from the drain port by the revolving scraper which rotates at a lower speed than that of the rotary disc.
Further, in Japanese Patent Laid-Open Publications No. 2002-248330 and 2001-198447, a continuous mixing device for mixing powder and liquid through a rotary mixing disc, in which a liquid is fed in atomized form for uniformly mixing the powder and the liquid, is suggested.
In Japanese Patent Laid-Open Publication No. 2001-65850, it is suggested that, in a method for producing a slurry mixture by mixing a powder such as a coal powder and a liquid such as water, the powder is fed into a screw pump to which the liquid is further supplied in the midstream of the screw pump so as to be mixed with the powder, and the pressure in the screw pump is first boosted and then lowered at an exhaust port for transforming the mixture into slurry.
Still further, the applicant of the present invention has also suggested, in Japanese Patent Laid-Open Publication No. 2000-246131, a dispersing apparatus comprising a casing capable of containing two or more materials therein and a grinding spindle installed in the casing. In that dispersing apparatus, pits and projections are formed on at least either one of the inner wall of the casing or the outer side surface of the grinding spindle, and by reciprocating the grinding spindle with respect to the casing to produce a narrow pressure in a clearance between the inner surface of the casing and the outer side surface of the grinding spindle, at least one out of the two or more materials can be dispersed.
However, because in any one of the above mixing devices and mixing methods the uniformity of the mixing is inadequate, or the available combination of powder and liquid to be mixed is limited, the mixing often does not achieve the quality desired.